In off-highway motor vehicles, such as agricultural tractors, vehicles for timber cutting, disbranching and transport in the terrain, etc., it is desirable to provide an operator seat which automatically adjusts horizontally on lateral tilting of the vehicle. Such a seat improves the comfort of the operator and protects from fatigue and back pain. Forward/backward tilting is a minor problem compared with lateral tilting. It is understood that the afore-mentioned vehicles are designed for slow movement, and that, consequently, seat adjustment need only to be relatively slow.
Self-levelling apparatus of the aforementioned kind are intended for mounting under the operator seat. In most vehicles the operator seat is in a cabin the dimensions of which are determined by the manufacturer of the vehicle independently of its provision with a self-levelling apparatus. For this and other reasons there are important restrictions in the space, in particular in respect of mounting height, available for mounting the self-levelling apparatus. This restriction also affects the choice and arrangement of the heavy duty drive mechanism for compensation of inclination.